Brave New Surfactant World Revisited by Thermoalkalophilic Lipases: SDS as a Potential Substrate Analog

Non-ionic surfactants stabilize the active conformation of thermoalkalophilic lipases by mimicking the lipid substrate while the role of anionic surfactants have not been studied at the structural level yet. In this study, we combined μs-scale molecular dynamic (MD) simulations and lipase activity assays to unravel the effect of sodium dodecyl sulfate (SDS), which is arguably the most widely used surfactant in protein characterization experiments, on the structure and function of thermoalkalophilic lipase family. We have performed simulations at two temperatures using six MD systems representing two equilibrium lipase conformers in three solvents. Because the open and closed conformations differ in geometry, recruiting both lipase forms provided a broader understanding of the molecular effect of SDS on thermoalkalophilic lipases. Low temperature simulations underscored the potential of SDS for maintaining the active form of thermoalkalophilic lipases through binding to the sn-1 acyl-chain binding pocket in the open conformation similar to non-ionic surfactants and also transforming the closed conformation to an open-like state. Consistent with MD findings, experimental analysis showed increased lipase activity upon SDS incubation at room temperature, suggesting SDS as an activator of this lipase family. High temperature simulations suggested a partial denaturating effect of SDS on thermoalkalophilic lipases monomers such that only surface structures including a β-hairpin motif which carries one of the catalytic amino acids were unfolded while the lipase core stayed intact regardless of SDS concentration or lid conformation. Simulations of lipase dimers, on the other hand, showed less flexible surface structures including the catalytically important β-hairpin, implying that intermolecular interactions within lipase dimers protects the structure against SDS-induced unfolding. Altogether, this study provides insights into the potential substrate mimicry by SDS for thermoalkalophilic lipase family, underscoring its potential use to favor open conformation.